Ecology of Highly Venomous Snakes: The Australian Genus Oxyuranus (Elapidae)

Abstract

The taipan, Oxyuranus scutellatus, is a large slender elapid of coastal tropical Aus- tralia. The small-scaled snake, 0. microlepidotus, is a similar snake from the arid zone. These are among the most highly venomous snakes in Australia, and probably in the world. We present information on body sizes, sexual size dimorphism, feeding habits, reproductive cycles, fecundity and inferred growth rates, based on dissection of museum specimens and observation of captive snakes. Adult snakes average approximately 1.5 m SVL in both Oxyuranus species, and males and females attain similar body sizes. Oxyuranus species are unique among Australian elapids in feeding exclu- sively upon endothermic prey. A wide variety of marsupials and rodents is taken: especially Rattus villosissimus and Antechinomys laniger by 0. microlepidotus, and Melomys sp., Mus musculus, Perameles nasuta and Rattus spp. by 0. scutellatus. The large body size, highly toxic venom and snap and release bite of Oxyuranus species may be adaptations to feeding on mammalian prey. Over recent decades, taipans have become more common relative to other large elapid species: we suggest that this may be due to the introduction of the toxic cane toad (Bufo marinus) as well as habitat modification by agriculture. Both Oxyuranus species are oviparous, with mating and oviposition from August to December. Fecundity (7-20 eggs), incubation period (60-80 days), and size at hatching (300-340 mm SVL) are similar in both species. Captive taipans show rapid growth, with sexual maturation as early as 16 months of age in males, and 28 months in females. In several aspects of morphology, ecology and behavior, 0. scutellatus is strongly convergent with an African elapid, Dendroaspis polylepis (the black mamba).